Recently, displays have shown remarkable progress. A variety of displays are briskly introduced to OA apparatuses such as PCs and word processors. These displays each have a structure in which a display element is interposed between transparent conductive films.
Currently, indium tin oxide (ITO) films constitute the mainstream of conductive transparent films since ITO films have excellent transparency, low resistance, improved etching properties, good adhesion to a substrate, as well as other qualities. Generally, ITO films are prepared by sputtering.
However, due to a relatively low moisture resistance, ITO films have such a disadvantage that the electric resistance value thereof increases by moisture. In addition, an ITO target which is used for producing an ITO film by sputtering tends to blacken by reduction. Therefore, changes in the properties of an ITO target with time have become a problem to overcome.
A transparent conductive film formed of indium oxide and zinc oxide which is superior to ITO films in moisture resistance, and has conductivity and light transmittance almost equivalent to that of ITO films, as well as a sputtering target formed of indium oxide and zinc oxide suitable for obtaining such transparent conductive film have been proposed (Patent Documents 1 and 2).
However, the transparent conductive film formed of indium oxide and zinc oxide is very prone to be etched by a weak acid. In addition, this film may be etched by an etching solution for a thin metal film. Therefore, in etching a thin metal film on the transparent conductive film, this transparent conductive film may also be etched. For this reason, this transparent conductive film is not suited for applications where a thin metal film on the transparent conductive film is selectively etched.
On the other hand, a transparent conductive film containing indium oxide and a lanthanide element is known to be useful as an electrode for organic EL devices or semi-transparent/semi-reflective LCDs.
An oxide of a lanthanide element has, however, no conductivity. Therefore, when a target is formed by mixing such an oxide with indium oxide, a target with a low conductivity is obtained. In addition, this target may encounter such problems as occurrence of extraordinary discharge during sputtering or blackening of the target surface. These problems cause the sputtering speed to be lowered.
Patent Document 1: JP-A-6-234565
Patent Document 2: JP-A-7-235219
Patent Document 3: JP-A-2004-68054
Patent Document 4: JP-A-2004-119272
Patent Document 5: JP-A-2004-139780
Patent Document 6: JP-A-2004-146136
Patent Document 7: JP-A-2004-158315
Patent Document 8: JP-A-2004-240091
Patent Document 9: JP-A-2004-294630
Patent Document 10: JP-A-2004-333882
An object of the invention is to provide a sputtering target which has a high conductivity and is free from problems such as extraordinary discharge or blackening of the target surface.